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Virginia Tech study of dynamic systems could lead to fewer falls and smoother rides

Virginia Polytechnic Institute And State University : 20 May, 2003  (Technical Article)
Harry Dankowicz's development of methods to predict changes in stability and design against instability in dynamic systems is based in the abstractions of differential equations, but aimed toward practical applications, such as improved ride comfort in automotive suspension systems or wearable devices that could reduce the number of fall-related injuries.
Dankowicz, who joined the Virginia Tech faculty as an assistant professor of engineering science and mechanics in 1999, has received a National Science Foundation Faculty Early Career Development Program Award worth $400,000 to support his research.

As a Fulbright scholar working on his Ph.D. in theoretical and applied mechanics at Cornell University, Dankowicz studied nonlinear dynamics and chaos theory. In 1996, as a research associate at the Royal Institute of Technology in Stockholm, Sweden, he turned his attention to models of human gait.

Simply said, nonlinear dynamics is the study of the behavior of physical systems, such as weather, biological organisms or complex mechanical systems, and their sensitivity to even small changes in initial conditions or parameters.

'A characteristic of such systems is their limited horizon of predictability,' Dankowicz said. 'Even minor errors in initial conditions can lead to significant deviation between predicted actions and reality.'

Particularly dramatic effects occur in systems with 'abrupt and discontinuous changes in system properties,' he said. 'In an automobile, for example, small impacts in the suspension system can result in large-amplitude vertical motion and an uncomfortable ride.'

The human gait, another mechanical system, is similarly subject to 'discontinuity-driven instabilities,' Dankowicz added. 'You're walking smoothly and your heel suddenly catches, that's a discontinuous change.'

If Dankowicz can develop a method to predict the effects of discontinuities on the stability of motion of a complex mechanical system, then he plans to develop design criteria that can reduce or prevent 'the detrimental effects of unintentional collisions between a mechanical system and its surrounding environment.'

In particular, Dankowicz is interested in the prevention of fall-related injuries, and one innovation he plans as part of his project is a model of scuffing contact between the human foot and the ground during gait. 'There are a number of low-impact conditions that can cause enough instability to result in a fall,' he said. In determining the role of friction in falling, for example, Dankowicz could use his computer model of the foot to analyze the effects of the composition of shoe soles or the roughness of floors.

This research could lead to the design of orthotic or prosthetic devices that would help reduce instability for people who are at risk of injuries from falls.

Investigating the human gait is just one aspect of his CAREER project, however, and Dankowicz hopes to create a predictive methodology that can be applied to a range of mechanical systems, such as automotive systems and industrial machinery.

An associate of the Virginia Tech Center for Biomedical Engineering, Dankowicz also has worked with researchers in the Virginia-Maryland Regional College of Veterinary Medicine on an exoskeletal device for equine limb disorders and injuries.

In addition, Dankowicz is working in the area of scoliosis treatment, developing computer-based tools to assist in corrective surgery for the spinal disorder.

Among his numerous scientific publications, Dankowicz has published three books. His textbook Multi-Body Mechanics and Visualization is based on a course he created that is taught at both KTH and Virginia Tech.

Dankowicz also will design a new course at Virginia Tech as part of his CAREER project. The junior-level course will give undergraduates experience in the design of experiments for measuring mechanical quantities with a focus on the behavior of complex mechanical systems.
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